The present invention relates to an improved structure of radio transmitter, and more particularly to such a radio transmitter which provides a learning function for duplicating other radio transmitters.
The base principle of the control of a remote controller is as follows: the transmitter produces a particular serial code subject to the setting of a set of key switches, the serial code is then transmitted to a remote receiver by means of a carrier medium (for example, infrared or radio) and then decoded by the receiver for operation control. Regular commercially available radio transmitters have no learning function. Therefore, if a person has three different radio remote control systems, three different transmitters are needed. Providing an infrared remote control system with a learning function can easily be achieved by installing a microcomputer capable of reading and memorizing encoding signal of other transmitters in the transmitter of the infrared remote control system and adding an infrared receiving element in the receiver of the infrared remote control system. However, it is difficult to provide a radio remote control system with a learning function because the signal encoding procedure is complicated and an identification code must be added for identification. A signal can be transmitted through the transmitter of a radio remote control system only when it is modulated by a high frequency carrier wave. Therefore, a transmitter with a learning function must have a radio receiving demodulating circuit. However, when learning, the frequency of the radio receiving demodulating circuit must be adjusted by an instrument. The transmitter of a radio remote control system generally comprises an encoder having pins at the data line thereof, and a set of control buttons respectively connected to the pins of the data line of the encoder, each control button define a particular control code, which determines the control function of the transmitter, and setting switch for example a DIP switch for setting an identification code. When power supply is connected, the encoder provides a serial code subject to the setting of the control buttons. In an infrared remote control system, the transmitter provides only function code but not identification code, and serial code directly drives an infrared diode to transmit the signal. In a radio remote control system, serial code is connected to a modulation and radio transmitting circuit.